Systems and methods provide for the rewriting and transformation of a code unit through an extensible, composable, set of code rewriters that can be implemented at various phases throughout the development, deployment, and execution of the code unit. The described systems and methods provide a powerful way for program developers and system administrators to implement code transformations at different stages throughout the development, deployment, and execution of programs that is largely independent of such programs and does not significantly increase the complexity of the source programs, compilers, or execution environments.